This invention relates to electric lamps and, more particularly, to a fuse wire for an electric lamp.
In the manufacture of electric lamps e.g. incandescent lamps, fuses e.g. of monel or nickel D wire are installed to interrupt excessive current flow therethrough to protect the lamp from damaging electric arcing. However upon filament failure and fuse burnout, one or more internal base arcs can develop, which can melt a hole through the lamp base and/or weld such base to the lamp socket with attendant risk of fire and personal injury.
To reduce such arcs, manufacturers have found it necessary to fill the lamp base with one or more insulative (sometimes porous) cement layers in an attempt to insulate the inside conductive surface of the base shell from fuse wire arcing. This type of solution requires additional steps in lamp manufacture and considerable expense and such base melt-through, though reduced, continues. For an example of a lamp base substantially filled with foamed cement, see U.S. Pat. No. 4,216,406 to Bjorkman et al. (1980).
A further shortcoming of the above conventional fuse wires is that in order to serve as a fuse for various lamps, e.g. 15 to 100 watts and higher, especially at 220 V to 245 V such fuse wires must be of a small diameter e.g. about 0.16 mm. Such small wire sizes are extremely difficult to handle in an automatic lamp production process, as the wire tends to kink and foul up under high speed machine manipulation.
Accordingly, such prior lamp fuses have not been satisfactory and there is a need and market for an improved lamp fuse which substantially overcomes the above prior art shortcomings.
By monel fuse wire as used herein is meant fuse wire of nickel/copper alloy in proportions well known in the art, e.g. a typical fuse wire material is monel 400 having a composition of nickel 63-70%, carbon 0.3% max., manganese 2.0% max., sulfur 0.24% max., silver 0.5% max. and a remainder of copper. All percentages noted herein are by weight unless otherwise stated.